If we were to ask a random group of '05-'09 Mustang GT owners for their thoughts on what the top-five first mods are for S197s, it's a safe bet that a cold-air intake system (better known as a CAI kit) would be included in each response.

Improving the air's volume and flow path into a new Mustang's Three-Valve engine is one of the best methods of increasing horsepower and torque. Installing a CAI system has proven to be the best way to achieve performance-enhancing air efficiency without spending millions.

It's sometimes hard to believe we've looked at so many different S197 cold-air kits over the last four years. Each system-whether installed and tested independently or with a group of additional budget-friendly bolt-on pieces-has supported the theory that cold air and improved airflow bump horsepower. Even so, one of the interesting factoids about the CAIs we've reviewed in the past is that none of them are approved by the California Air Resources Board, the mother of all clean-air organizations.

CARB has the responsibility of deciding which aftermarket performance parts are or aren't legal (smog-legal) for use in all 50 states. We don't know the criteria CARB uses to make its decisions, but based on what seems like its rejection of almost everything cool produced for 'Stangs (turbo systems, big-horsepower blowers, certain camshafts, nitrous, various headers and off-road exhaust pipes, and so on), we were surprised to hear that Ford Racing Performance Parts has once again beaten the odds.

So, if you are wondering about FRPP's latest CARB-approved winner (we've already detailed the company's smog-legal upgrade supercharger for Shelby GT500s), it's an all-new CAI for '05-'08 'Stangs! The new setup, formally referred to as the '05-'08 Mustang GT 85mm cold-air kit with premium CAL (PN M-9603-GTB; $669), is basically the same air-intake system that highlights the '08 Bullitt Mustang's engine bay. It's perfect for enthusiasts who want a modest performance gain without having to install noncompliant pieces (the key to achieving CARB's OK is a hydrocarbon trap inside the intake tube). Another plus for the kit that Editor Steve Turner has dubbed "the Bullitt CAI" is that Ford supports it with a factory warranty as long as the kit is installed by an authorized Ford or Lincoln Mercury dealer.

Fuel requirements are important elements of CAI upgrades. With the Bullitt kit in place, Mustangs that ran on lower-octane gas (87 or 89) before the upgrade are now married to a 91-octane minimum thanks to the airflow increase that the new system promotes. VIN-specific PCM calibrations that compensate for increased air and octane are available from FRPP, and they're loaded in a 'Stang's PCM using a handheld Pro-Cal flash tool.

For this effort, we're using a stock California Special edition of a Three-Valve '07 GT. The irony is somewhat appropriate, since Cali is the state that seems to always get shortchanged when it comes to CARB's decisions on performance parts.

After establishing a bone-stock baseline horsepower value on Extreme Automotive's chassis dyno, Saul "The Surgeon" Gutierrez handled the 10-minute bolt-on aspect of the test and reran the car to see what the Bullitt CAI is made of. As is par for the course with cold-air systems on stock S197s, the power gain was modest, but the system really does look sano. Thanks to that lining in its tube, the Bullitt CAI is the only kit out there for new Mustangs that CARB and Ford both endorse.